Don't know what it means, I don't call any constructor in Line
19. Then I tried to use "class" instead of "struct"
(http://ideone.com/ZI2Tn), it worked fine.
So what's wrong with that?

At first sight your code seems OK.
There is a well known compiler bug that makes it call the struct
constructor instead of its opCall. I think there is already a
pull request that fixes it in Bugzilla since some time (there are
more than one hundred of those open).
Bye,
bearophile